Demonstrate https://gist.github.com/brianoflan/e4b65bdb8505bc86ed069c51572fa527

demo_BASH_script_alt3.sh

#!/bin/bash

pre() {
  local f=$1 ;
  mkdir test_$f &> /dev/null ;
  ln -s ../functions.sh test_$f/functions.sh ;
  cat bash_script.sh.pre >  test_$f/bash_script.sh
  echo "$MAIN" >> test_$f/bash_script.sh ;
  cat bash_script.sh.post >> test_$f/bash_script.sh
}
post() {
  local f=$1 ;
  { bash test_$f/bash_script.sh ; echo $? ; } &> test_$f/out.txt ;
  e=0 ;
  echo "Testing $f()"
  diff -dbB test_$f/out.txt test_$f/out.txt.proper > $tmpf || e=$? ; cat $tmpf | perl -ne 'print "  $_"' ;
  if [[ $e -ne 0 ]] ; then
    echo "ERROR with $f(): '$e'." ; export errors="$errors $f" ;
  fi ;
  echo ;
}

main() {
  rm -rf demo_bash_scripts &>/dev/null ;
  [[ -d demo_bash_scripts ]] || mkdir demo_bash_scripts ;
  cd demo_bash_scripts && {
    tmpf=`mktemp "${TMPDIR:-/tmp}/tmp.XXXXXXXXXX"` ;
    export errors='' ;
cat > functions.sh <<'EOF'
#!/bin/bash

die() {
  local exit=$2 ;
  echo "$exit" | egrep '^[0-9][0-9]*$' &> /dev/null || exit=1 ;
  echo $1 ;
  exit $exit ;
}
execute() { # Notice and say so when a command has a non-zero exit status.
  local e=0 ;
  # echo "Executing." 1>&2 ;
  "$@" || e=$? ;
  [[ $e -eq 0 ]] || echo "ERROR: $e executing {$@}." 1>&2 ;
  return $e ;
}
vexecute() { # Verbose execute (say the command before running it).
  echo "Executing {$@}." 1>&2 ;
  execute "$@" ;
}
[[ $DEBUG -lt 2 ]] || echo "Sourced functions.sh ." 1>&2 ;
true ;

#
EOF
cat > bash_script.sh.pre <<'EOF'
#!/bin/bash

main() {
EOF
cat > bash_script.sh.post <<'EOF'
}
final() { # Never define final() in functions.sh - only ever define it in an actual script.
  [[ $DEBUG -lt 2 ]] || echo "final() { \$?: $? }" ; # Usually shows an exit code of 1 for some mysterious reason. QQQ
  echo final_in_script ;
}
trap final EXIT ;

cd $(dirname $0) && main "$@" || { e=$? ; echo "ERROR: '$e' with main in $0." ; exit $e ; } ;

#
EOF



# # #



f=debug ;
export MAIN="
  source ./functions.sh ;
" ;
pre $f ;
cat > test_$f/out.txt.proper <<'EOF'
Sourced functions.sh .
final() { $?: 1 }
final_in_script
0
EOF
export DEBUG=2 ;
post $f
export DEBUG=0 ;



# # #



f='return' ;
export MAIN="
  return 1 ;
" ;
pre $f ;
cat > test_$f/out.txt.proper <<EOF
ERROR: '1' with main in test_$f/bash_script.sh.
final_in_script
1
EOF
post $f



# # #



f=execute ;
export MAIN="
  source ./functions.sh ;
  execute bash -c 'exit 1'
  echo ;
" ;
pre $f ;
cat > test_$f/out.txt.proper <<'EOF'
ERROR: 1 executing {bash -c exit 1}.

final_in_script
0
EOF
post $f



# # #



f=execute_and_die ;
export MAIN="
  source ./functions.sh ;
  execute bash -c 'exit 1' || die 'Nay.'
" ;
pre $f ;
cat > test_$f/out.txt.proper <<'EOF'
ERROR: 1 executing {bash -c exit 1}.
Nay.
final_in_script
1
EOF
post $f



# # #



f=vexecute ;
export MAIN="
  source ./functions.sh ;
  vexecute bash -c 'exit 1'
  echo
" ;
pre $f ;
cat > test_$f/out.txt.proper <<'EOF'
Executing {bash -c exit 1}.
ERROR: 1 executing {bash -c exit 1}.

final_in_script
0
EOF
post $f



# # #



f=vexecute_and_die ;
export MAIN="
  source ./functions.sh ;
  execute bash -c 'exit 1' || die 'Nay.'
" ;
pre $f ;
cat > test_$f/out.txt.proper <<'EOF'
ERROR: 1 executing {bash -c exit 1}.
Nay.
final_in_script
1
EOF
post $f



# # #



# # #



    if [[ $errors ]] ; then
      echo -e "\n\n\nERRORS:$errors.\n" ;
      return 1 ;
    fi ;
  }
}
final() {
  cd .. ; rm -rf demo_bash_scripts.old &>/dev/null ; mv demo_bash_scripts demo_bash_scripts.old ;
}
trap final EXIT ;
main || exit $? ;

#